Variable air volume control apparatus

ABSTRACT

The invention relates to a variable air volume control apparatus which compensates an open area ratio to be in direct proportion to an opening ratio at a low opening ratio range according to an open angle of a damper blade to achieve accurate and precise air volume control. The variable air volume control apparatus includes a damper blade disposed rotatably within the duct for opening or closing an air flow path and an actuator for rotating the damper blade. The apparatus also includes an air flow path expansion mechanism having a curved surface for expanding the air flow path in accordance with an open angle of the damper blade. The invention allows obtaining the open area ratio in direct proportion to the opening ratio at the low opening ratio range through simple structural improvements, thereby improving linear characteristics of an air volume change ratio with respect to the opening ratio to more accurately and precisely control the air volume.

CLAIM OF PRIORITY

This application claims priority to the U.S. patent application Ser. No.11/715,255, filed Mar. 7, 2007, which claims the benefit of KoreanPatent Application No. 10-2006-0021944 filed on Mar. 8, 2006, and alsoclaims priority to the Korean Patent Application No. 2006-2149, filedMar. 8, 2007 in the Korean Intellectual Property Office, the disclosureof which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a variable air volume control apparatusfor adjusting the volume of air supplied indoors appropriately inaccordance with a set temperature of a room thermometer.

2. Description of the Related Art

In general, a variable air volume control apparatus is an importantcomponent in a variable air volume control system, which adjusts airvolume to change room temperature, thereby maintaining pleasant indoorenvironment as well as preserving energy.

In such a variable air volume control apparatus, an air volume changeratio curve in accordance with an opening ratio of a damper is animportant factor for adjusting the air volume according to temperaturechange indoors.

Therefore, the present invention aims to significantly improve the airvolume change ratio curve such that it is changed from a conventionalnon-linear form to a linear form to realize precise control of the airvolume. FIGS. 1 and 2 illustrate a conventional variable air volumecontrol apparatus, in which a circular plate-shaped damper blade 230 isinstalled with a shaft 232 in a cylindrical duct 210. The conventionalvariable air volume control apparatus controls air volume through afollowing process.

A room thermometer 250 (not shown in detail) installed indoors sensesroom temperature and transmits information thereof (a signal) to acontroller 260 (not shown in detail). The controller 260 which receivedthe information computes the information and currently set temperaturefrom the room thermometer 250 to calculate the air volume needed.

Then, the controller transmits a signal for an open angle correspondingto the air volume needed, to operational devices such as a motor or anactuator 240 which are then operated accordingly. Also, the controllermeasures the air volume at an inlet side via an air volume measurementdevice such as an anemometer or a differential pressure sensor installedat the inlet side and transmits the information (signal) to thecontroller 260.

The controller 260 receives the information (signal) from the air volumemeasurement device and rotates the shaft 232 of the operational deviceas much as, the excessive or deficient amount of air to adjust the openangle of the damper blade 230, thereby maintaining the air volumecorresponding to the information (signal) from the room thermometer 250.

However, as shown in FIG. 1, the conventional air volume controlapparatus 200 has drawbacks such as great imbalance between its openingratio and its open area ratio corresponding to the open angle of thedamper blade 230, air overflow, and friction between air flow and theinner surface of the duct 210. Thus, the air volume change ratio C isrepresented in a greatly deviating (distorted) curve rather than a line.

As shown in FIG. 3, the open area ratio curve B deviates greatly fromthe opening ratio line A, and thus the volume of air flowing throughcorresponding an open area is far from being in direct portion to thecorresponding opening ratio. Therefore, the air volume change ratio Cresults in a curve which greatly deviates from the opening ratio line A.

As seen from the air volume change ratio curve, in a low opening ratiorange of about 0 to 30%, i.e., in the range D1 of near closed state ofthe damper blade, the air volume change is too small with respect to thecorresponding change of the opening ratio, thus difficult to adjust theair volume in this range.

Also, in a high opening ratio range of about 70 to 100%, i.e., in therange D2 of near open state of the damper blade, the air volume changeis too small with respect to the corresponding opening ratio, thusdifficult to accurately and precisely adjust the air volume.

In addition, in the opening ratio range of 30% to 70%, the air volumechanges drastically with respect to even a small change in the openangle, i.e., the opening ratio of the damper blade, hindering precisecontrol of the air volume.

Therefore, in order to exclude the tendency of too small an air volumechange with respect to the opening ratio in the range D1 of near closedstate of the damper blade and achieve a linear form in the entire rangeof the opening ratio, in the conventional air volume control apparatusshown in FIG. 2, the damper blade 230 installed with the shaft 232inside the duct 210 is modified into an oval plate shape and the closedposition of the damper blade in the duct 210 is shifted about 30 degreesto an angle θ1 so that an adjustable range of angle θ2 is therebyshifted to be 30 degrees to 90 degrees.

Shifting the adjustable range of angle θ2 of the damper blade 230 to befrom 30 degrees to 90 degrees, where an adjustable range is from 0degrees to 60 degrees to yield 0% to 100% of air volume change, resultsin a drawback in which the adjustable range of angle is decreased by 33%from that with an adjustable range of 0 to 90 degrees to yield 0 to 100%of air volume change. This means that the adjustable range of angle istoo small to allow precise control of air volume.

Therefore, rather than reducing the adjustable angle range of thevariable air volume control apparatus 200, the adjustable angle range of0 to 90 degrees should be maintained to yield the air volume change of 0to 100% in order to more accurately and precisely control the airvolume.

Also, in order to change the air volume curve into a linear form, theopen area should be increased at the low opening ratio. This allowsobtaining a linear air volume change in proportion to the opening ratioof the damper blade at a low opening ratio, thereby accurately andprecisely controlling the air volume.

As confirmed above, the flow control damper is an essential componentfor adjusting the air volume introduced into the variable air volumecontrol apparatus in an air conditioning system adopting a variable airvolume control system. The capability of the flow control damper tolinearly control the air volume plays a determining role in efficientlyoperating the variable air volume control apparatus.

Recently, the controller for the variable air volume control apparatushas been developed into a finely-operated electronic type, which is usedin almost all air conditioning systems. However, if the variable airvolume control apparatus does not have a linear flow characteristics ofthe flow control damper operated by the actuator 240, precise control ofthe variable air volume control apparatus cannot be efficientlyrealized, regardless of excellent capabilities and control of thecontroller of the variable air volume control apparatus and the highlyaccurate and reliable flow sensor for sensing air volume change at aninlet side of the variable air volume control apparatus or constantfeedback control of the flow control damper by comparing and computingdifferential pressure signal from the flow sensor with the indoortemperature load change.

Air flows at the highest velocity in the central portion of a duct orconduit, and at a low velocity near the wall due to friction. Thus, whenthe damper blade is opened at the opening ratio of 100%, although thevelocity may somewhat change, the air volume flowing per unit of timeapproximates to 100% with substantially no inflow or outflow loss.

When the damper blade's opening ratio decreases by 50%, i.e., the damperblade 230 is biased at 45 degrees, the air volume is also supposed to bedecreased by 50%. However, the actual air volume turns out to be lessthan 50%. This is because when the damper blade 230 is biased at 50% (45degrees) in a cylindrical duct, the resultant open area ratio is toosmall at 29.29%, and thus the resultant air volume is also small atabout 40% (see FIG. 3).

Also, when the opening ratio of the damper blade is 30% or less, theresultant open area ratio is too small at 10% or less with too small anair volume, hindering precise control.

In addition, when the open angle of the damper blade 230 is 70% or more,the resultant open area is smaller than the directly proportional linewhereas too large a volume of air flows, hindering precise control.

As described above, in the conventional variable air volume controlapparatus 200, the air volume change with respect to the opening ratioof the damper blade 230 turns out to be a greatly deviating (distorted)curve C as shown in FIG. 3, rather than a line.

In FIG. 3, the graph shows the open area ratio and air volume changeratio with respect to the opening ratio, obtained by the aboveconventional variable air volume control apparatus.

Therefore, as shown in the graph in FIG. 3, with the conventional airvolume control apparatus 200, in the opening ratio range of 30% to 40%or less, the actual open area ratio curve B deviates greatly from theideal open area ratio, i.e., line A which is in direct proportion to theopening ratio of the damper blade 230. As a result, accurate control ofair volume is difficult.

Therefore, the conventional air volume control apparatus 200 cannotaccurately control the air volume introduced indoors, thus havingdifficulty in supplying fresh air indoors while consuming more energy.

In order to overcome such a problem, Korean Utility Model RegistrationNo. 0346769 (entitled “Dome Type Air Damper Unit”) has been suggested.This conventional dome type air damper unit has a cylindrical bodyhaving flanges at opposed ends thereof. Inside the body, a wing unit,connected to a control unit, is connected to a plurality of wings at oneside of the body, forming a dome-shape. The control unit adjusts theangle of the wings to operate the plurality of wings simultaneously,thereby changing an open area of an air outlet to adjust the air volume.

However, this conventional structure is structurally complex andexpensive, yielding a non-linear air volume characteristics curve.

A different conventional technology has been suggested in Korean UtilityModel Registration No. 0376799 (entitled “Variable Air Volume ControlApparatus”).

In this conventional variable air volume control apparatus, a shaft isdisposed movable back and forth and connected to a guide lever of adamper actuator disposed outside of the apparatus body and operated by aroom thermometer. Also, a pair of symmetrical air volume control dampersare split or joined in accordance with the movement of a pair of linksthat are connected to an end of the shaft. And an air conduit isinstalled to connect between an air inlet and a first air outlet, and isconnected to a mixed air outlet.

However, this structure is structurally complex, thus difficult tomanufacture, and expensive. Further, it uses a guide lever in a linkstructure, which makes noise and the resultant air volume change ratiocurve has non-linear characteristics.

A different structure from the above is disclosed in U.S. Pat. No.5,333,835 (entitled “Electric Motor Driven Air Valve”).

In this structure, a screw shaft is rotated by a motor to thereby move adamper blade connected to the screw shaft, adjusting the volume of airflowing between the open damper blade and the duct.

However, it is also difficult to accurately adjust the air volumeaccording to the orbit of the damper blade with this conventionalstructure which is expensive and difficult to manufacture due tostructural complexity.

SUMMARY OF THE INVENTION

The present invention has been made to solve the foregoing problems ofthe prior art and therefore an object of certain embodiments of thepresent invention is to provide a variable air volume control apparatuswith excellent performance, capable of accurately adjusting air volumethrough simple structural improvements, and is low-cost.

Another object of certain embodiments of the invention is to provide avariable air volume control apparatus in which an air flow path isopened in proportion to opening ratio of a damper blade at a low openingratio, thereby accurately adjusting air volume.

According to an aspect of the invention for realizing the object, thereis provided a variable air volume control apparatus for varying airvolume in a duct, including: a damper blade disposed rotatably withinthe duct for opening or closing an air flow path; an actuator forrotating the damper blade; an air flow path expansion mechanism having acurved surface for expanding the air flow path in accordance with anopen angle of the damper blade.

Preferably, the curved surface of the air flow path expansion mechanismexpands and compensates the air flow path such that an open area is indirect proportion to an opening ratio corresponding to an open angle ofthe damper blade.

Preferably, the air flow path expansion mechanism comprises a ringstructure installed on an inner surface of the duct, and the damperblade has a circumference the same as that of the ring structure.

Preferably, the ring structure has a circular inner periphery.

Preferably, the ring structure has an oval shape in which a horizontalor an axial diameter of the damper blade is larger than a verticaldiameter.

Preferably, the air flow path expansion mechanism is a part of the ductthat is constricted inward.

Preferably, the air flow path expansion mechanism is a part of the ductthat is bulged outward.

Preferably, the damper blade has an shaft shifted upward or downwardfrom a center of the duct.

Preferably, the damper blade is installed in a rectangular duct.

Preferably, the curved surface of the air flow path expansion mechanismis formed to compensate an open area of (θ/90)−(1−COS θ) at a lowopening ratio, where θ is an arbitrary angle at which damper blade openfrom a closed position of the damper blade.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 illustrates a conventional air volume control apparatus;

FIG. 2 illustrates another conventional air volume control apparatus;

FIG. 3 is a graph showing the open area ratio and the air volume changeratio with respect to the opening ratio, obtained by the conventionalvariable air volume control apparatus;

FIG. 4 is an overall configuration view illustrating a variable airvolume control apparatus according to the present invention;

FIG. 5 is a cross-sectional view illustrating the variable air volumecontrol apparatus according to the present invention;

FIG. 6 is a graph showing the open area ratio and the air volume changeratio with respect to the opening ratio, obtained by the variable airvolume control apparatus according to the present invention;

FIG. 7 is a cross-sectional view illustrating an alternative embodimentof the variable air volume control apparatus according to the presentinvention, in which an air flow path expanding mechanism having an ovalinner periphery;

FIG. 8 is a side sectional view illustrating another alternativeembodiment of the variable air volume control apparatus according to thepresent invention, in which the air flow path expansion mechanism is apart of the duct that is constricted inward;

FIG. 9 is a side sectional view illustrating yet another alternativeembodiment of the variable air volume control apparatus in which the airflow path expansion mechanism is a part of the duct that is bulgedoutward;

FIG. 10 illustrates a further another alternative embodiment of thevariable air volume control apparatus according to the presentinvention, in which a shaft of the damper blade is shifted downward; and

FIG. 11 is a side sectional view illustrating further anotheralternative embodiment of the variable air volume control apparatusaccording to the present invention including a rectangular duct.

FIG. 12 illustrates a graph showing the improved air volume change ratiowith respect to the opening ratio of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Preferred embodiments of the present invention will now be described indetail with reference to the accompanying drawings.

As shown in FIG. 4, the variable air volume control apparatus 1according to the present invention is installed inside a duct 10 throughwhich outside air is introduced and includes a flow sensor 20 forsensing air flow from the outside, a damper blade 30 for adjusting airflow introduced indoors from the outside, and an actuator 40 forrotating the damper blade 30.

Also, the variable air volume control apparatus 1 includes a roomthermometer 50 for detecting room temperature and a controller 60 forcontrolling the operation of the variable air volume control apparatus1.

The flow sensor 20, the actuator 40 and the room thermometer 50 areelectrically connected to the controller 60 to thereby be controlled.

Also, the variable air volume control apparatus 1 of the presentinvention includes an air flow path expansion mechanism 70 having acurved surface 70 a for expanding the airflow path according to an openangle θ of the damper blade 30 as the damper blade 30 is opened.

The air flow path expansion mechanism 70 provides an open area throughwhich air can flow as the damper blade construction 30 is opened, and tocontrol the air flow path in accordance with an open angle of the damperblade 30. The air flow path expansion mechanism 70 is positioned at apoint along the duct 10 so as to form constrictor portion with agenerally central rib portion and oppositely disposed side portionsextending sidewardly from the rib portion along the duct 10.

The rib portion projects inwardly relative to the side portions andgenerally transversely to the duct towards the center of the duct 10 toform a ridgeline to closely adjoin at least a portion of the outercircumference of the damper blade construction 30 when the damper bladeconstruction 30 is in its fully closed position.

The side portions include concavely curved surfaces 70 a facing inwardlytowards the duct 10, the curved surfaces 70 a meeting at the ridgelineand extending sidewardly from the rib portion along the duct 10.

The constrictor portion has an inner circumference at said ridgelineapproximately the same as the outer circumference of said damper bladeconstruction 30 such that, when said damper blade construction 30 is inits fully closed position, said constrictor portion and said damperblade construction 30 generally close the air flow path through theduct.

The curved surface 70 a of the air flow path expansion mechanism 70preferably expands and compensates the air flow path according to theopen angle of the damper blade 30. In particular, in a low opening ratiorange (hereinafter, referred to as the opening ratio of 0% to 30%), thecurved surface 70 a compensates for the area excluding an areacorresponding to “1−COS θ” from the air flow path in accordance with theopen area ratio in direct proportion to the open angle.

In addition, the air flow path expansion mechanism 70 preferably has aring structure 74 installed on an inner surface of the duct, and thedamper blade 30 has a circumference the same as an inner circumferenceof the ring structure 74.

That is, as shown in FIGS. 4 and 5, the air flow path expansionmechanism 70 is composed of a ring structure 74 installed on an innersurface of the duct 10, and the damper blade 30 has the innercircumference the same as the ring structure 74.

The air flow path expansion mechanism 70 can be installed on an innersurface of the duct 10 by a plurality of screws 72 penetrating throughthe duct 10 from the outside to fix the ring structure 74 on the innerside of the duct 10. The damper blade 30 is disposed inside the ringstructure 74, and the rotation shaft 32 penetrates through the ringstructure 74 and the duct 10 to enable rotation of the damper blade 30.

One end of the rotation shaft 32 is extended through the duct 10 and isconnected to an operator 40 to be rotated forward and backward.

In addition, the air flow path expansion mechanism 70 has a curvedsurface 70 a installed inside the duct 10 for expanding and compensatingthe air flow path for the area excluding an area corresponding to acosine function (1−COS θ) of the open angle θ of the damper blade 30.

The curved surface 70 a expands and compensates the open area for anarea corresponding to (θ/90)−(1−COS θ) at a low opening ratio, i.e., 0%to 30%. At an opening ratio greater than 30%, the open area is no longerexpanded or compensated. Thus at an opening ratio of up to 30%, the openarea ratio is expanded and compensated to have directly proportionalcharacteristics with respect to the opening ratio.

In addition, such a curved surface 70 a extends from a portion of theduct 10 corresponding to an end portion of the damper blade 30vertically positioned to a portion of the duct 10 corresponding to anend portion of the damper blade 30 horizontally positioned. In the upperregion with respect to the rotation shaft 32, the curved surface 70 a isinstalled in the air inlet side or the front side of the duct, and inthe lower region, it is installed in the air outlet side or the backsideof the duct 10.

When the damper blade 30 is opened at an arbitrary open angle θ at a lowopening ratio (0 to 30%), conventionally, the damper blade 30 is openedby an open area ratio corresponding to 1−COS θ. However, according tothe present invention, as shown in FIG. 4, the curved surface 70 a ofthe ring structure 74 compensates the open area ratio by (θ/90)−(1−COSθ) to obtain a linear open area ratio approximating to the openingratio.

As said damper blade construction 30 is operated within a low openingratio range of about 0% to 30%, the open air flow through the duct isincreased in an approximately linear relationship with the opening ratioas shown in FIGS. 6 and 12.

Further, said rib portion may have a height at said ridgeline in therange of about 10% to 40% of the radius of the duct 10.

Preferably, said rib portion may have a height at said ridgeline in therange of about 12.5% to 32.5% of the radius of the duct 10.

More preferably, said rib portion may have a height at said ridgeline inthe range of about 17.5% to 27.5% of the radius of the duct 10.

In addition, rather than having a ring structure 74 with a circularinner periphery, the air flow path expansion mechanism 70 can have aring structure 76 with an oval inner periphery in which the diameter ofthe portion of the shaft 32 of the damper blade is larger than thevertical diameter.

Such a structure as shown in FIG. 7 ensures more space in the air flowpath of the duct 10 while facilitating installation of the rotationshaft 32 of the damper blade.

In addition, the air flow path expansion mechanism 70 may preferably bea part of the duct 10 having a constricted part 78. As shown in FIG. 8,the duct 10 is machined to have the constricted part 78 constrictedinward of the duct 10. The curved surface 70 a of the air flow pathexpansion mechanism 70 expands and compensates for an area of the airflow path excluding the area corresponding to “1−COS θ” at a low openingratio range, i.e., 0 to 30%, in accordance with the open area ratio indirect proportion to the opening ratio.

Such a structure does not require an additional ring structure, and canbe formed by machining the duct 10, and thus can be adopted in thepresent invention without additional costs of material.

The constricted part 78 also has the curved surface 70 a foradditionally compensating the open area ratio by (θ/90)−(1−COS θ).

Alternatively; the air flow path expansion mechanism 70 can be astructure in which the duct 10 is machined to have a bulged part 80bulged outward of the duct 10. When the damper blade is open in an openangle θ at a low opening ratio (0 to 30%), conventionally, the damperblade is opened by an open area ratio corresponding to 1−COS θ. However,as shown in FIG. 9, with this bulged part 80 bulged outward of the duct10, the curved surface 70 a of the bulged part 80 compensates the openarea ratio by (θ/90)−(1−COS θ) to result in a linear open area ratioapproximating to the opening ratio:

Such a structure does not require an additional ring structure, and canbe formed by machining the duct 10, and thus can be adopted in thepresent invention without additional costs of material. Also, thestructure does not cause decrease in the air volume in the duct 10.

In addition, according to a certain embodiment of the present invention,the damper blade 30 has its rotation shaft 32 shifted upward or downwardfrom a center P of the duct 10.

As shown in FIGS. 10 (a) and 10(b), the rotation shaft 32 is shifted ina predetermined distance L downward from the center P of the duct 10.

In this case, the damper blade 30 may be a structure other than acircular plate, but the air flow path expansion mechanism 70 may stillbe a ring structure having an inner periphery the same as the outerperiphery of the damper blade 30, or a part of the duct 10 having aconstricted part.

In the above, a downwardly shifted position of the damper blade 30 ispresented, but an upwardly shifted position can also be adopted.

The invention is also effectively applicable to a duct 10′ having arectangular cross-section in addition to a circular cross-section. Inthis case, the air flow path expansion means 70 can be composed of firstand second curved structures 82 a and 82 b separated into upper andlower parts rather than a ring structure, and can be fixed to the upperand lower inner surfaces of the duct 10′, respectively.

As shown in FIG. 11, in such a structure, the first and second curvedstructures 82 a and 82 b have curved surfaces, respectively, forcompensating the conventional open area ratio of “1−COS θ” into the openarea ratio corresponding to “θ/90”, where each of the curved surfacescompensates the open area ratio by (θ/90)−(1−COS θ).

As shown in FIG. 4, the air volume control apparatus 1 with the abovedescribed configuration is operated in the range from the verticalposition of the damper blade 30 to completely block the air flow path at0 degrees to an arbitrary angle θ at which the damper blade 30 is openedto the horizontal position of the damper blade 30 to completely open theair flow path at 90 degrees.

As the air volume control apparatus 1 is operated as above, when thedamper blade 30 is open in an arbitrary angle θ (at a low opening ratioof about 0 to 30%), the actual open area ratio created by the damperblade 30 equals to a sum of the conventional open area ratiocorresponding to (1−COS θ) and an open area ratio corresponding toθ/90−(1−COS θ) compensated by the air flow expansion mechanism 70 at thearbitrary angle. As a result, this summed open area ratio corresponds toθ/90, which yields an open area ratio directly proportional to anarbitrary angle θ, i.e., opening ratio of the damper blade 30.

FIG. 6 illustrates a graph showing the improved open area ratio and airvolume change ratio with respect to the opening ratio by the presentinvention.

The open area ratio curve B′ shown in FIG. 6, improved by the presentinvention is in direct proportion to the opening ratio curve A at a lowopening ratio (0 to 30%).

FIG. 12 illustrates a graph showing the improved air volume change ratiowith respect to the opening ratio of the present invention.

In FIG. 12, curves C1, C2, and C3 respectively represent cases in whichthe rib portion has a height at the ridgeline equal to 10%, 22.5% and40% of the radius of the duct 10, and a curve C4 represents a case inwhich there is no rib portion in duct 10 according to the prior art.

As shown in FIG. 12, in a case which the rib portion has a height at theridgeline equal to 22.5% of the radius of the duct 10, the air volumechange ratio of curves C2 has an almost linear relationship with theopening ratio curve A at a low opening ratio.

Also, as shown in FIG. 12, the air volume change ratio of curves C1 andC3, improved by the present invention, is increased in an approximatelylinear relationship with the opening ratio curve A at a low openingratio (0 to 30%).

However, the air volume change ratio of curve C4, according to the priorart, deviates greatly from the opening ratio curve A.

As described above, in the present invention, when the damper blade 30is open in an arbitrary angle θ from a closed position completelyblocking the air flow path, for example, open at 9° (at the openingratio of 10%), the air flow path expansion mechanism 70 expands andcompensates the open area of the air flow path by 9/90−(1−COS 9°). Whenthe damper blade 30 is further opened up to 27° (the opening ratio of30%), the air flow expansion mechanism 70 expands and compensates theopen area of the air flow path by 27/90−(1−COS 27°), thereby increasingair volume.

In addition, at the opening ratio of 30% (27° or more, the presentinvention yields the open area ratio curve that is similar to the openarea ratio curve B with respect to the opening ratio of the damper blade30 without any compensation.

As described above, the open area ratio with respect to the openingratio is improved significantly from the conventional curve B to havedirect proportional characteristics at an opening ratio of 30% or less,i.e., an open angle of 27° or less.

Thereby, at an opening ratio of 0 to 50%, the air volume change ratiowith respect to the opening ratio is improved to have linearcharacteristics to achieve more accurate and precise air volume control.

As set forth above, certain embodiments of the present invention attainsthe open area ratio approximate to opening ratio through simplestructural improvements by the air flow path expansion mechanism,thereby achieving more accurate and precise air volume control.

Also, according to certain embodiments of the invention, installing thesimple air flow path expansion mechanism allows accurate control of theair volume and a low-cost air volume control apparatus having excellentcapabilities.

Certain exemplary embodiments of the invention have been explained andshown in the drawings as presently preferred. The invention may,however, be embodied in many different forms and should not be construedas limited to the embodiments set forth herein. While the presentinvention has been shown and described in connection with the preferredembodiments, it will be apparent to those skilled in the art thatmodifications and variations can be made without departing from thespirit and scope of the invention as defined by the appended claims.

1. A variable air volume control apparatus for varying air volume in aduct having a passageway therethrough defining an air flow path,comprising: a damper blade construction that has an outer circumferenceand is disposed within the duct to be rotatable between a fully closedposition generally transverse to the duct and a fully open positiongenerally aligned with the duct for opening or closing the air flow paththrough the duct; an actuator for rotating the damper blade; an air flowpath expansion mechanism for providing an open area through which aircan flow as the damper blade construction is opened and to control theair flow path in accordance with an open angle of the damper blade, saidmechanism positioned at a point along the duct to form constrictorportion with a generally central rib portion and oppositely disposedside portions extending sidewardly from said rib portion along the duct,said rib portion projecting inwardly relative to said side portions andgenerally transversely to the duct towards the center of the duct toform a ridgeline to closely adjoin at least a portion of the outercircumference of said damper blade construction when said damper bladeconstruction is in its fully closed position, said side portionsincluding concavely curved surfaces facing inwardly towards the duct,said curved surfaces meeting at said ridgeline and extending sidewardlyfrom said rib portion along the duct, said constrictor portion having aninner circumference at said ridgeline approximately the same as theouter circumference of said damper blade construction such that, whensaid damper blade construction is in its fully closed position, saidconstrictor portion and said damper blade construction generally closethe air flow path through the duct; whereby, as said damper bladeconstruction is operated within a low opening ratio range of about 0% to30%, the open air flow through the duct is increased in an approximatelylinear relationship with the opening ratio and said rib portion has aheight at said ridgeline in the range of about 10% to 40% of the radiusof the duct.
 2. The variable air volume control apparatus according toclaim 1, wherein said rib portion has a height at said ridgeline in therange of about 12.5% to 32.5% of the radius of the duct.
 3. The variableair volume control apparatus according to claim 1, wherein said ribportion has a height at said ridgeline in the range of about 17.5% to27.5% of the radius of the duct.